The present invention relates to wireless power supply systems, and more particularly to systems and methods for transferring power to devices at a range of distances.
Many conventional wireless power supply systems rely on inductive power transfer to convey electrical power without wires. A typical inductive power transfer system includes an inductive power supply that uses a primary coil (or a transmitter) to wirelessly transfer energy in the form of a varying electromagnetic field and a remote device that uses a secondary coil (or a receiver) to convert the energy in the electromagnetic field into electrical power.
Many conventional wireless power supplies operate efficiently at fairly close range, for example where there is less than an inch between the charger and the remote device. Some developers have focused on producing wireless power supply systems that can effectively provide wireless power at a greater distance. This greater range can be useful where it is not possible to position the remote device near the charger. For example, where an inductive charger is installed underneath a table, the greater range is helpful to effectively power a device sitting on top of the table.
One approach for providing greater range is accomplished by designing power supplies that operates at essentially a fixed z-distance. Such mid range power supplies are well known and can be designed by utilizing isolated re-resonator coils on the primary and secondary side. One issue with these mid range power supplies is that they have a fairly narrow range at which power can be delivered effectively. This makes mid range power supplies impractical where the desired distance of wireless power transfer varies or is unknown. For example, a mid range power supply to be mounted under a table or countertop is impractical because the thicknesses of the tables and countertops are not uniform and the variations in thicknesses are large enough to be outside the range of tolerances for a given mid range wireless power supply design. Designing and selling different mid range power supplies to transfer wireless power to different distances is not cost effective or practical.